autofs: fix dev ioctl number range check

The count of miscellaneous device ioctls in fs/autofs4/autofs_i.h is wrong.

The number of ioctls is the difference between AUTOFS_DEV_IOCTL_VERSION_CMD
and AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD (14) not the difference between
AUTOFS_IOC_COUNT and 11 (21).

[kusumi.tomohiro@gmail.com: fix typo that made the count macro negative]
 Link: http://lkml.kernel.org/r/20160831033420.9910.16809.stgit@pluto.themaw.net
Link: http://lkml.kernel.org/r/20160812024841.12352.11975.stgit@pluto.themaw.net


Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>